Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
Turn Hot Water Tap On
Gain access to interface PCB
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the AC voltage between Pin 4 (Brown) and Pin 3 (Blue) on connector CN2 on the interface PCB.
Expect mains voltage.